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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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828                               ALASKAN GLACIER STUDIES
In contrast to this tidal cliff is the projecting south half of the ice front, a low, sloping surface, with crevasses nearly healed, easy to traverse and thinly veneered with ablation 1 moraine. In front of it is a small area of slumping debris from which much water emerges, proving that part of the flat is underlain by buried ice blocks. Indeed black ice is revealed in places. This projection of the glacier on the western side is due partly to the protection furnished by the morainic cover and partly to the fact that the salt water has undercut the eastern cliff and caused it to retreat faster.
Serpentine Glacier is fed by four or five moderate-sized tributaries from high cirques on Mt. Gilbert, by one from the 6683 foot peak west of Cascade Glacier, and by a large tributary which descends steeply from the slopes of Mt. Muir and enters on the western side about half a mile from the terminus. Farther south on the slopes of Mt. Muir there are also twin cascading glaciers, formerly tributaries of the Serpentine, which now terminate about 3000 feet above sea level.
The white surface of Serpentine Glacier is diversified by a number of medial moraine stripes; and there is a pronounced lateral moraine ridge (PI. CXXXIII) on the eastern side, left standing by recent retreat. The glacier slopes moderately and is not as severely crevassed as Barry Glacier, although in the last few hundred feet of descent to the water's edge the slope is so steep that travel upon this part of the ice surface was impossible.
Besides the rock ledges beneath the eastern edge of the tidal ice cliff, and the bare rock slopes along the eastern margin of the glacier, there are strong rock ledges near the western margin, one of them cut through by a shallow, smoothly-scoured gorge with vertical walls but with no stream at present. Its upper end hangs in' the air, and below its terminus are stony stream deposits.
Slight Change. Between the time of its discovery by the Harriman Expedition in 1899 and our own studies in 1910, the terminus of the Serpentine Glacier has not changed appreciably except in thinning and slight shortening described by Grant and Higgins, on the basis of observations and photographs in 1905 and 1909. Gannett mapped the glacier in a general way in 1899 (PI. CXXIX, A) and Higgins in more detail ten years later. It is shown upon our 1910 map (Fig. 45).
Moraines. There is clear evidence that not many years ago Serpentine Glacier extended at least a mile farther than now, and that it ended in Harriman Fiord with a tidal ice front 1$ miles or more in length. This is proved by terminal and lateral moraine deposits and by a barren zone near the terminus of the glacier, containing only scattered small shrubs and mosses.
The terminal moraine varies considerably in character, and most of it is free from slumping. The western part is a broad, gently-undulating surface rising perhaps 50 feet above sea level, but being higher and more hmnmocky on the southeastern border. There is much bare rock, mostly angular and without striae. The eastern portion is a submerged bar extending completely across the mouth of the cove, except for two narrow gaps. At high tide this moraine bar is completely covered; but at low tide nearly the whole of it is exposed. Inside the bar is the cove in which Serpentine Glacier terminates, and in this cove the water is from 30 to 51 feet deep, while at the entrance the greatest depth is only 1% feet. Since the formerly expanded glacier spread out into the bulb shape, it will be seen that the site of this cove inside the crescentic terminal moraine, where there was melting of clean ice without enough d6bris to fill the shallow inden-